BuddyPress.org

Create a child theme of bp-default theme.
Re: background color = You need to override default style by changing the background color and image from
`body {
background: #eaeaea url( ../images/background.gif ) top left repeat-x;
…
}`
to something like the following which you should add in child theme’s style.css
`body {
background: #fffff none;
}`
which you adjust to taste.

Re: header size change height set in default theme by adding this to your child theme’s style.css
#header{
height: 200px;
}
adjust to taste.